In the processing and packaging of semiconductor devices, conductive bumps are formed for use in providing electrical interconnections. For example, such bumps may be provided for: (1) use in flip-chip applications, (2) use as stand-off conductors, (3) wire looping applications, (4) test points for testing applications, amongst others. Such conductive bumps may be formed using various techniques. One such technique is to form the conductive bumps using wire, such as on a wire bonding machine or a stud bumping machine.
Numerous techniques for forming conductive bumps on a wire bonding machine or bumping machine are disclosed in U.S. Pat. No. 7,229,906 (entitled “METHOD AND APPARATUS FOR FORMING BUMPS FOR SEMICONDUCTOR INTERCONNECTIONS USING A WIRE BONDING MACHINE”) and U.S. Pat. No. 7,188,759 (entitled “METHOD FOR FORMING CONDUCTIVE BUMPS AND WIRE LOOPS”), both of which are incorporated by reference in their entirety.
FIG. 1 illustrates an exemplary sequence of forming a conductive bump on a wire bonding machine or bumping machine. At Step 1, free air ball 100a is seated at the tip of bonding tool 102. As will be understood by those skilled in the art, prior to Step 1, free air ball 100a had been formed on an end of wire 100 that hangs below the tip of bonding tool 102 using an electronic flame-off device or the like. Wire clamp 104 is also shown at Step 1 in the open position. As will be understood by those skilled in the art, wire 100 is provided by a wire spool on the machine (not shown). Wire 100 extends from the wire spool through wire clamp 104 (and through other structures not shown) and through bonding tool 102.
After free air ball 100a is formed (prior to Step 1), wire 100 is drawn upwards (e.g., using a vacuum control tensioner or the like) such that free air ball 100a is seated at the tip of bonding tool 102 as shown at Step 1 of FIG. 1. At Step 2, bonding tool 102 (along with other elements of a bond head assembly including wire clamp 104) is lowered and free air ball 100a is bonded to bonding location 106 (e.g., a die pad of semiconductor die 106). As will be understood by those skilled in the art, the bonding of free air ball 100a to bonding location 106 may utilize ultrasonic energy, thermosonic energy, thermocompressive energy, XY table scrub, combinations thereof, amongst other techniques.
After free air ball 100a is bonded to bonding location 106 at Step 2 (where the bonded free air ball may now be termed bonded ball 100b), with wire clamp 104 still open, bonding tool 102 is raised to a desired height as shown by the upward arrow in Step 3. This height may be referred to as a separation height (as shown in Step 3 of FIG. 1, bonding tool 102 has been raised such that bonded ball 100b is no longer seated in the tip of bonding tool 102). At Step 4, with wire clamp 104 still open, bonding tool 102 is moved in at least one horizontal direction (e.g., along the X axis or Y axis of the machine) to smooth the top surface of bonded ball 100b. Such smoothing provides a desirable top surface for a conductive bump, and also weakens the connection between bonded ball 100b and the rest of the wire to assist in the separation therebetween. At Step 5, bonding tool 102 is raised to another height (which may be referred to as the wire tail height), and then wire clamp 104 is closed. Then at Step 6, bonding tool 102 is raised to break the connection between bonded ball 100b (which may now be termed conductive bump 100c) and the remainder of wire 100. For example, bonding tool 102 may be raised to an EFO height which is a position at which an electronic flame-off device forms a free air ball on wire tail 100d of wire 100.
Forming conductive bumps using such conventional techniques may result in certain deficiencies. Such deficiencies may include, for example: premature separation between bonded ball 100b and the rest of wire 100 due to the smoothing at step 4; potential short wire tail conditions because of such premature separation; potential long wire tail conditions; and undesirably reduced smoothing of bonded ball 100b in an attempt to avoid such premature separation.
Conductive bump 100c shown at Step 6 may be used as a stand-off in a wire looping process known as stand-off stitch bonding (“SSB”). Improved wire looping techniques utilizing conductive bumps, including improved SSB techniques would be desirable.